Semiconductor device and method for producing the same

ABSTRACT

A gate electrode is formed on a substrate via a gate insulating film. The gate insulating film includes a high dielectric constant film containing a metal, oxygen and hydrogen, and a lower barrier film formed below the high dielectric constant film and containing a metal, oxygen, silicon and nitrogen.

RELATED APPLICATIONS

This application is a divisional of application Ser. No. 10/122,366filed Apr. 16, 2002 now U.S. Pat. No. 6,642,131.

This application claims priority from U.S. Provisional Application No.60/299,478, filed on Jun. 21, 2001, and Japanese Patent Application No.2001-395734, filed Dec. 27, 2001.

BACKGROUND OF THE INVENTION

The present invention relates to a semiconductor device and a method forproducing the same, in particular, a high dielectric constant film usedfor a gate insulating film.

With recent technological advance with respect to high integration andhigh speed in semiconductor devices, miniaturization of MOSFETs has beenunder development. When the thickness of a gate insulating film is beingreduced to achieve the miniaturization, problems such as an increase ofa gate leak current due to tunneling current are caused. In order tosuppress this problem, there has been research on an approach toincrease a physical thickness while realizing a small SiO₂ equivalentthickness (hereinafter, referred to as “EOT”) by using gate insulatingfilms made of high dielectric constant material such as hafnium oxide(HfO₂) and zirconium oxide (ZrO₂) (hereinafter, referred to as “high-kgate insulating films”).

For example, a method for forming a conventional high-k gate insulatingfilm described in U.S. Pat. No. 6,013,553 is as follows. First, an oxidelayer such as a SiO₂ layer is formed on a silicon substrate, and then ametal film made of zirconium or hafnium is deposited on the oxide layerby sputtering or plasma CVD. Thereafter, the metal film is subjected toan oxynitridation treatment with gas such as NO to form a high-k gateinsulating film made of zirconium oxynitride (ZrO_(x)N_(y)) or hafniumoxynitride (HfO_(x)N_(y)).

However, in the conventional high-k gate insulating film, when heathistory is applied by a high temperature treatment during the productionprocess, the high dielectric constant material constituting the gateinsulating film is crystallized, so that the electrical conductivity viathe resultant crystal grain boundaries or the defect level increasesleak current. That is to say, the thermal stability of the conventionalhigh-k gate insulating film is insufficient.

SUMMARY OF THE INVENTION

Therefore, with the foregoing in mind, it is an object of the presentinvention to provide a semiconductor device employing a thermally stablegate insulating film having a high relative dielectric constant.

In order to achieve the object, a semiconductor device of the presentinvention includes a gate insulating film formed on a substrate; and agate electrode formed on the gate insulating film, and the gateinsulating film includes a high dielectric constant film containing ametal, oxygen and silicon; and a lower barrier film formed below thehigh dielectric constant film and containing the metal, oxygen, siliconand nitrogen.

According to the semiconductor of the present invention, the highdielectric constant film constituting the gate insulating film containssilicon, so that the high dielectric constant film is prevented frombeing crystallized by a high temperature treatment in the productionprocess (e.g., a heat treatment for activating impurities at about 900°C.). Therefore, in a finished semiconductor device, the high dielectricconstant film remains mostly amorphous, so that leak current can besuppressed from occurring in the high-k gate insulating film.Consequently, the thermal stability of the high-k gate insulating filmcan be improved, and therefore a semiconductor device having excellentheat resistance can be realized, and the process margin in theproduction of a semiconductor device can be increased.

According to the semiconductor of the present invention, the lowerbarrier film is present below the high dielectric constant film in thegate insulating film, so that the high dielectric constant film can beprevented from reacting with the substrate. Moreover, the lower barrierfilm contains the same metal as in the high dielectric constant film, sothat the relative dielectric constant of the lower barrier film can beincreased, and thus the relative dielectric constant of the entire gateinsulting film can be increased.

In the semiconductor device of the present invention, it is preferablethat the gate insulating film includes an upper barrier film formedabove the high dielectric constant film, and the upper barrier filmcontains the metal, oxygen and nitrogen.

This prevents the gate electrode material and the high dielectricconstant film material from being diffused to each other. Moreover, theupper barrier film contains the same metal as in the high dielectricconstant film, so that the relative dielectric constant of the upperbarrier film can be increased, and thus the relative dielectric constantof the gate insulting film as a whole can be increased.

In the semiconductor device of the present invention, it is preferableto satisfy0.23≦y/(x+y)≦0.90

when the composition of the high dielectric constant film is expressedas M_(x)Si_(y)O, where M, O and Si represent the metal, oxygen andsilicon, respectively, and X>0 and y>0.

This ensures the thermal stability of the high-k gate insulating filmagainst a heat treatment at about 900° C. while keeping the relativedielectric constant of the high-k gate insulting film sufficient.

In the semiconductor device of the present invention, it is preferableto satisfy0.23≦y/(x+y)≦0.30

when the composition of the high dielectric constant film is expressedas M_(x)Si_(y)O, where M, O and Si represent the metal, oxygen andsilicon, respectively, and X>0 and y>0.

This ensures the thermal stability of the high-k gate insulating filmagainst a heat treatment at about 900° C. while keeping the reliabilitylife of the high-k gate insulting film sufficient.

In the semiconductor device of the present invention, it is preferableto satisfyx/(x+y)≧0.10

when the metal is hafnium or zirconium, and the composition of the lowerbarrier film is expressed as M_(x)Si_(y)ON, where M, O, Si and Nrepresent the metal, oxygen, silicon and nitrogen, respectively, and x>0and y>0.

This ensures that the relative dielectric constant of the lower barrierfilm can be increased.

In the semiconductor device of the present invention, the gate electrodemay be a metal gate electrode.

A first method for producing a semiconductor device of the presentinvention includes the steps of forming a high dielectric constant filmcontaining a metal, oxygen and a predetermine substance on a substrate;performing a heat treatment with respect to the high dielectric constantfilm to diffuse silicon from the side of the substrate into the highdielectric constant film, thereby forming a silicon-containing highdielectric constant film; and forming a conductive film for serving as agate electrode on the silicon-containing high dielectric constant film.

According to the first method for producing a semiconductor device, apredetermined substance can be desorbed from the high dielectricconstant film by performing a heat treatment with respect to the highdielectric constant film containing the predetermined substance, so thatsilicon is diffused in the high dielectric constant film through thethus formed vacancies and thus a silicon-containing high dielectricconstant film can be formed. Therefore, silicon can be contained in thehigh dielectric constant film efficiently, and the vacancies eventuallydisappear, so that the silicon-containing high dielectric constant filmcan become dense. The silicon-containing high dielectric constant filmhardly is crystallized by a high temperature treatment in the productionprocess, so that the silicon-containing high dielectric constant filmremains mostly amorphous after a device is complete. As a result, leakcurrent can be suppressed from occurring in the gate insulating filmincluding the silicon-containing high dielectric constant film, that is,the high-k gate insulating film. Consequently, the thermal stability ofthe high-k gate insulating film can be improved, and therefore asemiconductor device having excellent heat resistance can be realized,and the process margin in the production of a semiconductor device canbe increased.

In the first semiconductor method of the present invention, it ispreferable the predetermined substance is hydrogen.

This ensures that silicon can be diffused in the high dielectricconstant film.

It is preferable that the first semiconductor method includes forming aninsulating film containing silicon, nitrogen and the predeterminedsubstance on the substrate before the step of forming the highdielectric constant film; and that the step of performing a heattreatment with respect to the high dielectric constant film comprisesdiffusing silicon contained in the insulating film into the highdielectric constant film, and forming a lower barrier film by diffusingthe metal contained in the high dielectric constant film into theinsulating film.

This ensures that silicon can be diffused in the high dielectricconstant film. Furthermore, the high dielectric constant film or thesilicon-containing high dielectric constant film can be prevented fromreacting with the substrate. Moreover, the lower barrier film containsthe same metal as in the silicon-containing high dielectric constantfilm, so that the relative dielectric constant of the lower barrier filmcan be increased, and thus the relative dielectric constant of the gateinsulting film as a whole can be increased.

In the first method for producing a semiconductor device, it ispreferable that the step of forming a high dielectric constant filmcomprises forming a high dielectric constant film by CVD employing asource precursor containing the metal and the predetermined substance.

Thus ensures that a high dielectric constant film containing thepredetermined substance is formed.

In the first method for producing a semiconductor device, it ispreferable that the step of forming the high dielectric constant filmincludes forming the high dielectric constant film by CVD employing asource precursor containing the metal and a source gas containing thepredetermined substance.

Thus ensures that a high dielectric constant film containing thepredetermined substance is formed.

In the first method for producing a semiconductor device, it ispreferable that the step of forming the high dielectric constant filmincludes forming the high dielectric constant film by PVD employing atarget containing the metal in an atmosphere containing thepredetermined substance.

Thus ensures that a high dielectric constant film containing thepredetermined substance is formed.

A second method for producing a semiconductor device of the presentinvention includes the steps of forming a high dielectric constant filmcontaining a metal, oxygen and hydrogen on a substrate; performing aheat treatment with respect to the high dielectric constant film todiffuse silicon from the side of the substrate into the high dielectricconstant film, thereby forming a silicon-containing high dielectricconstant film; and forming a conductive film for serving as a gateelectrode on the silicon-containing high dielectric constant film.

According to the second method for producing a semiconductor device,hydrogen can be desorbed from the high dielectric constant film byperforming a heat treatment with respect to the high dielectric constantfilm containing hydrogen, so that silicon is diffused in the highdielectric constant film through the thus formed vacancies and thus asilicon-containing high dielectric constant film can be formed.Therefore, silicon can be contained in the high dielectric constant filmefficiently, and the vacancies eventually disappear, so that thesilicon-containing high dielectric constant film can become dense. Thesilicon-containing high dielectric constant film hardly is crystallizedby a high temperature treatment in the production process, so that thesilicon-containing high dielectric constant film remains mostlyamorphous after a device is complete. As a result, leak current can besuppressed from occurring in the gate insulating film including thesilicon-containing high dielectric constant film, that is, the high-kgate insulating film. Consequently, the thermal stability of the high-kgate insulating film can be improved, and therefore a semiconductordevice having excellent heat resistance can be realized, and the processmargin in the production of a semiconductor device can be increased.

It is preferable that the second method for producing a semiconductordevice includes forming an insulating film containing silicon, nitrogenand hydrogen on the substrate before the step of forming the highdielectric constant film; and that the step of performing a heattreatment with respect to the high dielectric constant film includesdiffusing silicon contained in the insulating film into the highdielectric constant film, and forming a lower barrier film by diffusingthe metal contained in the high dielectric constant film into theinsulating film.

This ensures that silicon can be diffused in the high dielectricconstant film. Furthermore, the high dielectric constant film or thesilicon-containing high dielectric constant film can be prevented fromreacting with the substrate. Moreover, the lower barrier film containsthe same metal as in the silicon-containing high dielectric constantfilm, so that the relative dielectric constant of the lower barrier filmcan be increased, and thus the relative dielectric constant of theentire gate insulting film can be increased.

In the second method for producing a semiconductor device, it ispreferable that the step of forming the high dielectric constant filmincludes forming the high dielectric constant film by CVD employing asource precursor containing the metal and hydrogen.

Thus ensures that a high dielectric constant film containing hydrogencan be formed.

In the second method for producing a semiconductor device, it ispreferable that the step of forming the high dielectric constant filmincludes forming the high dielectric constant film by CVD employing asource precursor containing the metal and a source gas containinghydrogen.

Thus ensures that a high dielectric constant film containing hydrogencan be formed.

In the second method for producing a semiconductor device, it ispreferable that the step of forming the high dielectric constant filmincludes forming the high dielectric constant film by PVD employing atarget containing the metal in an atmosphere containing hydrogen.

Thus ensures that a high dielectric constant film containing hydrogencan be formed.

In the first or the method for producing a semiconductor device, it ispreferable that the metal is hafnium or zirconium.

This ensures that the relative dielectric constant of thesilicon-containing high dielectric constant film can be increased.

In the first or the second method for producing a semiconductor device,it is preferable that the method includes the step of forming an upperbarrier by nitriding a surface of the silicon-containing high dielectricconstant film between the step of performing a heat treatment withrespect to the high dielectric constant film and the step of forming aconductive film.

This prevents the gate electrode material and the high dielectricconstant film material from being diffused to each other. Moreover, theupper barrier film contains the same metal as in the high dielectricconstant film, so that the relative dielectric constant of the upperbarrier film can be increased, and thus the relative dielectric constantof the entire gate insulting film can be increased.

In the first or the second method for producing a semiconductor device,it is preferable that the method includes the step of forming an upperbarrier by nitriding a surface of the high dielectric constant filmbetween the step of forming a high dielectric constant film and the stepof performing a heat treatment with respect to the high dielectricconstant film.

This prevents the gate electrode material and the high dielectricconstant film material from being diffused to each other. Moreover, theupper barrier film contains the same metal as in the high dielectricconstant film, so that the relative dielectric constant of the upperbarrier film can be increased, and thus the relative dielectric constantof the entire gate insulting film can be increased.

In the first or the second method for producing a semiconductor device,it is preferable that the temperature for the heat treatment in the stepof performing the heat treatment with respect to the high dielectricconstant film is 600° C. or more and 850° C. or less.

This ensures that the predetermined substance or hydrogen can bedesorbed from the high dielectric constant film, and that silicon can bediffused in the high dielectric constant film.

In the first or the second method for producing a semiconductor device,it is preferable to satisfy T≦6.69·y/(x+y)+749.4, when the compositionof the silicon-containing high dielectric constant film is expressed asM_(x)Si_(y)O, where M, O and Si represent the metal, oxygen and silicon,respectively, and x>0 and y>0, and the maximum temperature in theproduction process is expressed as T [° C.].

This ensures the thermal stability of the high-k gate insulating filmhaving the silicon-containing high dielectric constant film.

In this case, it is preferable that the gate electrode is made of amaterial containing silicon, and y/(x+y)≦0.30 is satisfied.

This enables a sufficient reliability life for the high-k gateinsulating film having the silicon-containing high dielectric constantfilm.

In the first or the second method for producing a semiconductor device,it is preferable that the gate electrode is a metal gate electrode, andthe method includes the step of performing a heat treatment with respectto the substrate after the step of forming a conductive film.

This allows the defects in the high-k gate insulating film having thesilicon-containing high dielectric constant film to be reduced further.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectional view of a semiconductor device according toa first embodiment of the present invention.

FIG. 2 is a graph showing the relationship between the amount of Siadded to HfO₂ and the crystallization temperature of HfO₂ and thetemperature that guarantees thermal stability of HfO₂.

FIG. 3 is a diagram showing the allowable range of the composition of Hfsilicate that can maintain the thermal stability obtained correspondingto various maximum process temperatures.

FIG. 4 is a graph showing the relationship between the amount of Siadded to a HfO₂ film and the relative dielectric constant of the HfO₂film.

FIG. 5 is a graph showing the relationship between the amount of Siadded to a HfO₂ film and the reliability life of the HfO₂ film.

FIG. 6 is a graph showing the relationship between the amount of Siadded to a HfO₂ film and the thermal stability and the reliability ofthe HfO₂ film.

FIGS. 7A to 7C are cross-sectional views showing the processes in amethod for producing a semiconductor device according to a secondembodiment of the present invention.

FIGS. 8A to 8C are cross-sectional views showing the processes in amethod for producing the semiconductor device according to the secondembodiment of the present invention.

FIGS. 9A to 9D are views illustrating the behavior resulted from PDA inthe method for producing the semiconductor device according to thesecond embodiment of the present invention.

FIG. 10 is a graph showing the results of measurement by TDS regardinghydrogen being desorbing from the HfO₂ film due to a heat treatment.

FIG. 11 is a graph showing the results of C-V measurement after a heattreatment with respect to a H-containing HfO₂ film formed by CVD usingHf-t-butoxide in the method for producing a semiconductor deviceaccording to the second embodiment of the present invention.

FIG. 12 is a graph showing the result of C-V measurement after a heattreatment with respect to a H-free HfO₂ film formed by CVD using asource that does not contain hydrogen as a comparative example.

FIG. 13 is a graph showing the results of a comparison in the thermalstability between the case where the H-containing HfO₂ film (the secondembodiment of the present invention) is used and the case where theH-free HfO₂ film (comparative example) is used in a MOS capacitor havinga layered structure of Si substrate/SiN film/HfO₂ film/polysilicon film.

FIG. 14 is a graph showing the relationship between the physicalthickness of a HfO₂ film that has just formed and the leak current aftera MOS capacitor is complete in the case where PDA in the method forproducing a semiconductor device of the second embodiment of the presentinvention is performed with respect to the HfO₂ film, which is aninsulating film of the MOS capacitor.

DETAILED DESCRIPTION OF THE INVENTION

First Embodiment

Hereinafter, a semiconductor device of a first embodiment of the presentinvention, more specifically, a MISFET will be described with referenceto the accompanying drawings.

FIG. 1 shows the cross-sectional structure of a semiconductor device ofa first embodiment.

As shown in FIG. 1, a gate electrode 12 is formed on a silicon substrate10 via a gate insulating film 11. An impurity diffusion layer 13 servingas a source region or a drain region is formed on both sides of the gateelectrode 12 in the silicon substrate 10. The gate insulating film 11includes a high dielectric constant film 11 a made of insulative metaloxide, a lower barrier film 11 b formed below the high dielectricconstant film 11 a, and an upper barrier film 11 c formed above the highdielectric constant film 11 a.

More specifically, the high dielectric constant film 11 a is formed of asubstance in which silicon is contained in hafnium oxide (HfO₂) having ahigh relative dielectric constant, that is, a silicon-containing hafniumoxide (Hf_(x)Si_(y)O₂, where x>y>0). The lower barrier film 11 b forpreventing a reaction between the silicon substrate 10 and the highdielectric constant film 11 a is made of, for example, a siliconoxynitride film containing hafnium. The upper barrier film 11 c forpreventing a reaction between the high dielectric constant film 11 a andthe gate electrode 12 is made of, for example, a silicon-containinghafnium oxide film containing nitrogen. That is to say, the lowerbarrier film 11 b and the upper barrier film 11 c are high dielectricconstant barrier films. The gate electrode 12 is made of, for example, apolysilicon film doped with phosphorus.

The high dielectric constant film 11 a may contain nitrogen. When thephysical thickness of the gate insulating film 11 is about 4 nm, thephysical thickness of the high dielectric constant film 11 a is about 2nm, the physical thickness of the lower barrier film 11 b is slightlysmaller than 1 nm, and the physical thickness of the upper barrier film11 c is slightly larger than 1 nm. All of the high dielectric constantfilm 11 a, the lower barrier film 11 b, and the upper barrier film 11 care amorphous.

In this embodiment, silicon is contained in the HfO₂ film that serves asthe high dielectric constant film 11 a for the purpose of ensuring thethermal stability of the high dielectric constant film 11 a. In otherwords, the high dielectric constant film 11 a containing silicon ishardly crystallized (or is only partially crystallized and remainsamorphous) when being subjected to a heat treatment at a hightemperature, so that an increase of leak current due to crystal grainboundaries or defect level can be suppressed. Hereinafter, thisembodiment will be described more specifically with reference to theaccompanying drawings.

FIG. 2 shows the relationship between the amount of silicon (Si) addedto HfO₂ and the crystallization temperature of HfO₂ and the thermalstability guarantee temperature of HfO₂. The crystallization temperaturerefers to the temperature at which an amorphous state started to changeinto a crystalline state. In other words, since a change of the statestarts at the crystallization temperature, the entire substance (HfO₂)is not necessarily crystallized immediately even if the temperatureexceeds the crystallization temperature.

In FIG. 2, the horizontal axis shows the ratio X₁ (% representation) ofthe number of Si atoms contained in HfO₂ per unit volume (hereinafter,referred to as “Si concentration”) to the sum of the Si concentrationand the number of Hf atoms contained in HfO₂ per unit volume(hereinafter, referred to as “Hf concentration”). In other words, thefar left end in the horizontal axis (X₁=(Si concentration/(Siconcentration+Hf concentration))×100=0%) indicates HfO₂ that contains noSi, and the far right end in the horizontal axis (X₁=(Siconcentration/(Si concentration+Hf concentration))×100=100%) indicatesSiO₂ that contains no Hf. The vertical axis shows the temperature.

As shown in FIG. 2, the crystallization temperature and the thermalstability guarantee temperature of HfO₂ increase with the ratio X₁, thatis, the amount of added Si. In other words, the addition of silicon toHfO2 increases the thermal stability of HfO₂. This is because anincrease of the Si amount makes it easy that Si-containing HfO₂, thatis, a Hf silicate material remains amorphous, and as a result, theentire HfO₂ film hardly is crystallized and remains amorphous.

Herein, the thermal stability guarantee temperature refers to theannealing temperature at which a drastic increase of leak current startsto occur in an insulating film made of HfO₂ when an annealing treatmentis performed with respect to a MOS capacitor structure having theinsulating film for 30 seconds in N₂ gas at 1 atm with a rapid thermalprocess (TP) apparatus. Therefore, at temperatures below the thermalstability guarantee temperature, the leak current and the capacitance inthe MOS capacitor structure employing the Si-containing HfO₂ filmindicates an ideal value. On the other hand, at temperatures above thethermal stability guarantee temperature, the leak current in the MOScapacitor structure increases by about three orders due to a drasticincrease of defects locally occurring in the Si-containing HfO₂ film. Atthis point, the capacitance in an accumulation state in a C-V(capacitance-voltage) measurement diverges, and therefore it becomesimpossible to measure the capacitance of the MOS capacitor. In otherwords, at temperatures above the thermal stability guaranteetemperature, the MOS capacitor structure employing the Si-containingHfO₂ film cannot serve as a capacitor.

When the ratio X₁ is 70% or more, the substantially entire Si-containingHfO₂ film can be kept amorphous even at high temperatures, so that evenif the film is subjected to a high temperature process at 1200° C., leakcurrent can be suppressed. If the ratio X₁ is at least 23%, the crystalsproduced when the Si-containing HfO₂ film is crystallized aremicrocrystalline, and the film as a whole is predominantly in theamorphous state. Therefore, leak current can be suppressed even if thefilm is subjected to a high temperature process of 900° C. Herein, thecase where the material to be used is mostly amorphous, or the casewhere the material to be used contains crystallites to the extent thatmakes substantially no influence on the thermal stability, that is, theheat resistance, is also regarded as being amorphous.

As shown in FIG. 2, the straight line showing the range of the processtemperature that can be used in the process for producing asemiconductor device and the range of the Si concentration in theSi-containing HfO₂ film can be defined as T=6.69 X₁+749.4, where X₁represents the Si concentration/(Si concentration+Hf concentration)×100and T [° C.] represents the thermal stability guarantee temperature(more specifically, when a polysilicon electrode is used). In otherwords, it is necessary that the process temperature and the Siconcentration are in the range below T=6.69·X₁+749.4. More specifically,when the value of X₁, that is, the composition of the Si-containing HfO₂is determined, the process temperature has to be in the temperaturerange of not more than the thermal stability guarantee temperature Tcorresponding to the predetermined value of X₁. On the other hand, whenthe maximum temperature of the process is determined, it is necessary toselect a Si-containing HfO₂ film, that is, a Hf silicate film to whichSi is added such that X₁ is larger than a value of X₁ when the maximumtemperature is used as the thermal stability guarantee temperature T. Inthe case of the structure of the semiconductor device of this embodimentshown in FIG. 1, the Si concentration can be determined as describedabove, with respect to, for example, either the entire gate insulatingfilm 11 or a region about 2 nm below the interface with the gateelectrode 12 in the gate insulating film 11 in view of a contact withthe gate electrode 12.

FIG. 3 shows the allowable range of the composition (X₁) of Hf silicatethat can ensure the thermal stability, which was obtained correspondingto various maximum process temperatures based on the relationship(experiment results) shown in FIG. 2. As shown in FIG. 3, for example,when the maximum process temperature is about 900° C. (e.g., in theprocess in which polysilicon is used as the electrode material), X₁should be at least 23% in order to prevent a drastic increase of leakcurrent due to defects or the like and ensures the thermal stability.

FIG. 4 shows the relationship between the amount of Si added to the HfO₂film and the relative dielectric constant of the HfO₂ film. In FIG. 4,the upper horizontal axis shows X₁=(Si concentration/(Siconcentration+Hf concentration))×100 as described above, which indicatesthe Si amount. The lower horizontal axis shows X₂=(Hf concentration/(Siconcentration+Hf concentration))×100 as described above, which indicatesthe Hf amount. The vertical axis shows the relative dielectric constantof the HfO₂ film. □ shows the value obtained by an actual measurement ofthe relative dielectric constant.

As shown in FIG. 4, when X₁ is 0% (that is, when the film is the HfO₂film, which contains no Si), the relative dielectric constant of theHfO₂ film is about 24, which is the maximum. The relative dielectricconstant decreases as the Si amount in the HfO₂ film increases, but therelative dielectric constant is substantially constantly about 11 whenX₁ is between 30% and 90%. When the Si amount in the HfO₂ film furtherincreases and exceeds 90%, the relative dielectric constant graduallydecreases again, and the relative dielectric constant is about 3.9 whenX₁ is 100%/o (that is, when the film is the SiO₂ film, which contains noHf). Therefore, when X₁ is 90% or less, that is, when X₂ is 10% or more,a Hf silicate film having a comparatively high and stable relativedielectric constant can be realized.

According to the results shown in FIGS. 2 to 4 described above, it isimportant to set X₁=(Si concentration/(Si concentration+Hfconcentration))×100 in the high dielectric constant film 11 a made ofsilicon-containing HfO₂ to 23% or more and 90% or less in order that thehigh dielectric constant film 11 a (which may be a stacked structure ofa combination of the high dielectric constant film 11 a, the lowerbarrier film 11 b and/or the upper barrier film 11 c, instead of thehigh dielectric constant film 11 a) has the thermal stability whilehaving a high relative dielectric constant.

X₁=(Si concentration/(Si concentration+Hf concentration))×100 has thesame meaning as (y/(x+y))×100 when the composition of the highdielectric constant 11 a is represented as Hf_(x)Si_(y)O (where x>0, andy>0). Similarly, X₂=(Hf concentration/(Si concentration+Hfconcentration))×100 has the same meaning as (x/(x+y))×100. X₁ and X₂show the relationship between the Si concentration and the Hfconcentration, so that also when Hf silicate to be used contains N inthe form of Hf silicate nitride, or when it contains other elements suchas Cl, F and H, the above description employing X₁ and X₂ is effective.

FIG. 5 shows the relationship between the amount of Si added to the HfO₂film and the reliability life of the HfO₂ film (period of time untilbreakdown occurs). In FIG. 5, the upper horizontal axis shows X₁=(Siconcentration/(Si concentration+Hf concentration))×100 as describedabove, which indicates the Si amount. The lower horizontal axis showsX₂=(Hf concentration/(Si concentration+Hf concentration))×100 asdescribed above, which indicates the Hf amount. The vertical axis showsthe reliability life of the HfO₂ film. □ shows the value obtained by anactual measurement of the reliability life.

More specifically, various samples of MOS capacitors having Hf silicatefilms having different compositions are prepared, and a TDDB (timedependent dielectric breakdown measurement) test is performed toestimate the long term reliability life of the Hf silicate films underthe conditions of an incidence of failure of 100 ppm, an insulating filmarea (MOS area) of 0.1 cm², a temperature of 100° C., an applied voltageV_(G)=−1V, and EOT (SiO₂ equivalent thickness)=1.5 nm. The results areshown in FIG. 5. Herein, the composition of the Hf silicate in eachsample varies in the range from SiO₂, which contains no Hf to HfO₂,which contains no Si. Each sample is formed on a p-type substrate, and aconstant negative stress voltage is applied to the electrodes, setting0V on the substrate side.

More specifically, the insulating film area of each sample used in theTDDB test is in the range from 3×10⁻⁷ cm² to 5×10⁻⁵ cm². To obtain thereliability life at an insulating film area of 0.1 cm², the followingequation based on the assumption that defects in the insulating film aredistributed according to the Poisson distribution was used:

The reliability life of the insulating film area 1

=the reliability life of the insulating film area 2×(insulating filmarea 2/insulating film area 1) ^((1/β)), where β is a Weibull gradient.The temperature during the TDDB test is in the range from roomtemperature to 100° C. To obtain the reliability life at a temperatureof 100° C., activation energy of the reliability life obtained inadvance with respect to a temperature change was used. To obtain thereliability life at an incidence of failure of 100 ppm, a Weibullgradient β was obtained based on a Weibull plot obtained by the TDDBtest, and then the approximate straight line of an intrinsic breakdownwas extended. Furthermore, in the TDDB test, V_(G) larger than 1 V as anabsolute value is used, whereas in order to obtain the reliability lifeat V_(G)=−1 V, experiment data of the reliability life corresponding toa real electric field Eox (real) that is obtained from an equation of(V_(G) (at the time of the TDDB test)−Vfb)/Tph, where Vfb is a flat bandvoltage, and Tph is the physical thickness of the entire insulatingfilm, were extended by the straight-line approximation.

According to the results shown in FIG. 5 obtained using theabove-described method, when X₁ (upper horizontal axis) is 30% or less,that is, when X₂ is 70% or more, the reliability life of the Hf silicatefilm is 10 years or more. The results shown in FIG. 5 are those obtainedby estimating the reliability life on the lower voltage side withrespect to the real electric field Eox (real). The results obtained byestimating the reliability life on the lower voltage side with respectto the V_(G) itself at the time of the TDDB test or the effectiveelectric field Eox (effective) obtained by an equation of (V_(G) (at thetime of TDDB test)−Vfb)/EOT exhibit the similar tendency.

According to the results shown in FIGS. 2 to 4, when thermal stabilityand a high relative dielectric constant are targeted, it is preferableto set X₁=(Si concentration/(Si concentration+Hf concentration))×100 to23% or more and 90% or less. On the other hand, according to the resultsshown in FIG. 5, when X₁ is 30% or less, the reliability life of 10years or more can be obtained. That is to say, when reliability as wellas thermal stability and a high relative dielectric constant aretargeted, the preferable range of X₁ is 23% or more and 30% or less.However, in the case of a process that does not require a hightemperature treatment after a gate insulating film is formed, such as areplacement gate process (process that allows a gate electrode to beformed after formation of source and drain regions by using a dummygate), more specifically, in the case of a process that does not requirea heat treatment at 750° C. or more after a gate electrode is formed, itis sufficient to target only reliability, so that the preferable rangeof X₁ is 30% or less.

FIG. 6 shows the relationship between the amount of Si added to the HfO₂film and the thermal stability and the reliability of the HfO₂ film.

As shown in FIG. 6, the preferable range of the structure (composition)of the high-k gate insulating film made of a HfO₂ film containing Si orthe process temperature can be divided roughly into three regions. To bespecific, when only thermal stability is targeted, the preferable rangeis below T=6.69·X₁+749.4. In order to obtain a comparatively highrelative dielectric constant in the maximum process temperature of 900°C. as well, X₁ has to be set to 23% or more and 90% or less. In the caseof a process that does not require a high temperature treatment after agate insulating film is formed, such as a case using a replacement gate,it is sufficient to target only reliability, so that it is sufficient toset X₁ to 30% or less. Furthermore, in a conventional Si process, when ahigh-k material is used as the gate insulating film material instead ofSiON, and Poly-Si or SiGe or the like is used as the gate electrodematerial, that is, when annealing for activating impurities is performedat a comparatively high temperature after a gate insulating film isformed, it is necessary to target both thermal stability andreliability, so that the range that is below T=6.69·X₁+749.4 andsatisfies that X₁ is 30% or less is preferable. In this case, when themaximum process temperature is 900° C., X₁ has to be set to 23% or moreand 30% or less. It should be noted that 900° C. is a typicaltemperature in annealing for activating impurities contained in a sourceregion, a drain region or an electrode.

As described above, according to the first embodiment, the highdielectric constant film 11 a included in the gate insulating film 11 isa HfO₂ film containing silicon, so that the high electric constant film11 a can be prevented from being crystallized by a high temperaturetreatment in the production process. Therefore, in a finishedsemiconductor device, the high dielectric constant film 11 a remainsmostly amorphous, so that leak current can be suppressed from occurringin the gate insulating film 11, that is, the high-k gate insulatingfilm. Consequently, the thermal stability of the gate insulating film 11can be improved, so that a semiconductor device having excellent heatresistance can be realized, and the process margin in the production ofthe semiconductor device can be increased.

Furthermore, according to the first embodiment, the lower barrier film11 b containing silicon, nitrogen and oxygen is present below the highdielectric constant film 11 a in the gate insulating film 11, so thatthe high dielectric constant film 11 a and the silicon substrate 10 canbe prevented from being reacted with each other. Herein, the lowerbarrier film 11 b prevents the silicon substrate 10 from being oxidizedby oxygen in the high dielectric constant film 11 a. That is to say,when an oxide film having a relative dielectric constant substantiallyequal to that of a SiO₂ film is formed on the surface of the siliconsubstrate 10 as an interface layer, the relative dielectric constant ofthe gate insulating film 11 as a whole decreases significantly, andtherefore the lower barrier film 11 b is provided.

Furthermore, according to the first embodiment, the lower barrier film11 b contains the same metal as in the high dielectric constant film 11a, specifically, hafnium, so that the relative dielectric constant ofthe lower barrier film 11 b can be higher than that of a regular siliconoxynitride film, so that the relative dielectric constant of the gateinsulating film 11 as a whole can be made higher. More specifically, asshown in FIG. 4, when hafnium is introduced into the lower barrier film11 b in a ratio of 10% or more with respect to silicon (that is X₂≧10%),so that the relative dielectric constant of the lower barrier film 11 bcan increase effectively. On the other hand, as shown in FIG. 4, whenthe silicon content in the lower barrier film 11 b is too large (morespecifically, X₁≧90%), the relative dielectric constant decreasesdrastically. In other words, it is very effective to set the Hfconcentration in the lower barrier film 11 b to be higher than X₂=0%even to a slight extent in order to reduce the EOT of the entire gateinsulating film 11.

Furthermore, according to the first embodiment, the upper barrier film11 c is present in a portion above the high dielectric constant film 11a in the gate insulating film 11, so that the material of the gateelectrode 12 (polysilicon in this embodiment) is prevented from beingmixed with the material of the high dielectric constant film 11 a (e.g.,hafnium) more than necessary, and thus a reduction of the relativedielectric constant of the gate insulating film 11 can be suppressed. Inthis case, the barrier effect of the upper barrier film 11 c can beimproved by allowing the upper barrier film 11 c to contain nitrogen.The relative dielectric constant of the upper barrier film 11 c can beincreased by allowing the upper barrier film 11 c to contain the samemetal, hafnium, as the high dielectric constant film 11 a, and thus therelative dielectric constant of the entire gate insulating film 11 canbe increased.

In the first embodiment, it is preferable to set X₁=(Siconcentration/(Si concentration+Hf concentration))×100 in the highdielectric constant film 11 a (which may be a stacked structure of acombination of the high dielectric constant film 11 a, the lower barrierfilm 11 b and/or the upper barrier film 11 c, instead of the highdielectric constant film 11 a) to 23% or more and 90% or less. By doingthis, the relative dielectric constant of the high dielectric constantfilm 11 a can be increased and even if a heat treatment at about 900° C.is performed, the high dielectric constant film 11 a can be suppressedfrom being crystallized, so that an increase of leak current due todefects or the like can be prevented. In other words, the thermalstability of the gate insulating film 11 can be ensured while therelative dielectric constant of the gate insulating film 11 is keptsufficient. In this case, it is more preferable to set X₁ in the highdielectric constant film 11 a to 23% or more and 30% or less. By doingthis, in addition to the above-described advantages, a sufficientreliability life of the high dielectric constant film 11 a, that is, thegate insulating film 11 can be obtained. When the maximum processtemperature is reduced to be significantly low by the use of areplacement gate or the like, merely setting X₁ to 30% or less ensuresthe thermal stability of the gate insulating film 11 while ensuringsufficient relative dielectric constant and reliability life of the gateinsulating film 11.

In the first embodiment, HfO₂ is used as the high dielectric constantmaterial included in the gate insulating film 11, but instead of thismaterial, ZrO₂, TiO₂, Ta₂O₅, La₂O₃, CeO₂, Al₂O₃, or BST (bariumstrontium titanium oxide) or the like can be used. Alternatively,ternary oxide such as Hf_(x)Al_(y)O₂, where x>0, and y>0) can be used.Alternatively, metal silicate in which Si atoms are contained in theabove-listed metal oxides can be used.

In the first embodiment, the lower barrier film 11 b and the upperbarrier film 11 c are provided, but there may be no need of providingthe lower barrier film 11 b and/or the upper barrier film 11 c,depending on the selection of the material of the gate electrode 12.

In the first embodiment, a polysilicon electrode is used as the gateelectrode 12, but instead of this, a so-called metal gate electrode madeof a metal film such as a stacked film of a TiN film and a Al film (TiNfilm as the lower film), a Ta film, a TiN film or a TaN film can beused. If a metal film such as a TiN film or TaN film is used as themetal gate electrode material, Si or Ge can be mixed with the metalfilm.

Second Embodiment

Hereinafter, a method for producing a semiconductor device of a secondembodiment of the present invention, specifically, a method forproducing a MISFET will be described with reference to the accompanyingdrawings.

FIGS. 7A to 7C and 8A to 8C are cross-sectional views showing theprocesses of a method for producing a semiconductor device of the secondembodiment.

First, as shown in FIG. 7A, an insulating film for isolation (not shown)is formed on a p-type silicon (100) substrate 20, and a device formingregion is segmented. Then, standard RCA cleaning and diluted HF cleaningare performed with respect to the surface of the silicon substrate 20.Thereafter, a silicon nitride film (Si₃N₄ film) 21A having a thicknessof about 0.7 nm is formed on the silicon substrate 20 with NH₃ gas at atemperature of about 700° C. In this process, sufficient hydrogen iscaptured in the Si₃N₄ film 21A. The Si₃N₄ film 21A eventually becomesthe lower barrier film 21 (see FIG. 7C).

Next, as shown in FIG. 7B, a hafnium oxide (HfO₂) film 22A having athickness of about 5 nm is formed on the silicon substrate 20 by CVD(chemical vapor deposition) employing a source precursor containinghafnium. More specifically, nitrogen (N₂) gas as a carrier gas isallowed to pass through Hf-t-butoxide (C₁₆H₃₆HfO₄), which is a liquid Hfsource, to bubble the Hf-t-butoxide to evaporate the Hf-t-butoxide.Then, a RTCVD (rapid thermal CVD) treatment is performed at atemperature of about 500° C. while the N₂ gas containing the evaporatedHf-t-butoxide and dry oxygen (O₂) gas as an oxidizing agent are suppliedto a chamber in which the silicon substrate 20 (wafer) is placed, andthus a HfO₂ film 22A is formed.

In this process, the Si₃N₄ film 21A is oxidized by the O₂ gas as anoxidizing agent, and turns into a SiON film 21B. The SiON film 21B hasbarrier properties for preventing a reaction between the siliconsubstrate 20 and the HfO₂ film 22A and contains sufficient hydrogen. Inthis embodiment, after the Si₃N₄ film 21A is formed on the siliconsubstrate 20, the Si₃N₄ film 21A is oxidized during the formation of theHfO₂ film 22A to form the SiON film 21B. However, without forming theSi₃N₄ film 21A, the SiON film 21B can be directly formed by nitridingthe surface of the silicon substrate 20 with N₂O gas before forming theHfO₂ film 22A.

In the process shown in FIG. 7B, hydrogen (H) contained in the Hf sourceis spontaneously captured in the HfO₂ film 22A. On the other hand,carbon (C) contained in the Hf source is oxidized by the O₂ gas as anoxidizing agent, so that it is exhausted in the form of CO or CO₂ fromthe chamber. In the chamber, in addition to Hf, O, C, and H, which areconstituent elements of the Hf source, N₂ gas is present, but the N₂ gasis very inert at temperatures below about 500° C., so that an influenceof the N₂ gas can be ignored.

When the HfO₂ film 22A was analyzed by a SIMS method (secondary ion massspectroscopy), it was found that primary elements constituting the HfO₂film 22A were Hf and O. In the HfO₂ film 22A, 3×10¹⁹ to 4×10²⁰ carbonatoms/cm³ and 5×10²⁰ to 4×10²¹ hydrogen atoms/cm³ were contained.

Next, a heat treatment (hereinafter, referred to as PDA (post depositionanneal)) is performed with respect to the HfO₂ film 22A. PDA isperformed, for example, in a nitrogen atmosphere at about 700° C. for 30seconds. Now, changes occurring in the stacked structure of the SiONfilm 21B and the HfO₂ film 22A by performing PDA will be described indetail with reference to FIGS. 9A to 9D. As described above, beforeperforming PDA, as shown in FIG. 9A, the SiON film 21B and the HfO₂ film22A contain hydrogen. When PDA is performed, as shown in FIG. 9B,hydrogen is desorbed from the SiON film 21B and the HfO₂ film 22Aefficiently in the form of hydrogen gas. As a result, as shown in FIG.9C, vacancies (white circles in FIG. 9C) are formed in the SiON film 21Band the HfO₂ film 22A. Then, as shown in FIG. 9D, silicon contained inthe silicon substrate 20 or the SiON film 21B is diffused into the HfO₂film 22A through the vacancies, and Hf contained in the HfO₂ film 22A isdiffused into the SiON film 21B. As a result, as shown in FIG. 7C, asilicon-containing HfO₂ film 22 having high thermal stability is formed,and a lower barrier film 21 made of the Hf-containing SiON film having ahigh relative dielectric constant can be formed. The silicon-containingHfO₂ film 22 is formed by making the HfO₂ film 22A dense by thediffusion of silicon. The specific composition of the lower barrier film21 is the same as the lower barrier film 11 b of the first embodiment.

In other words, vacancies obtained by desorbing hydrogen from the HfO₂film 22A and the SiON film 21B has the effect of promoting mutualdiffusion of Hf and Si. In this case, setting the temperature for PDA toabout 700° C. brings about double effects, that is, an effect ofpromoting hydrogen desorption to facilitate formation of vacancies andan effect of facilitating diffusion of Hf or Si. As a result, one PDAallows Si to be captured in the HfO₂ film 22A to form thesilicon-containing HfO₂ film 22 having high thermal stability, andallows Hf to be captured in the SiON film 21B to form the lower barrierfilm 21 (Hf-containing SiON film) having a high relative dielectricconstant. Therefore, the thermal stability of a gate insulating film 25(see FIG. 8C) as a whole including the silicon-containing HfO₂ film 22and the lower barrier film 21 can be improved, and consequently therelative dielectric constant of the gate insulating film 25 as a wholecan be increased.

Next, the surface of the silicon-containing HfO₂ film 22 is nitridedlightly, so that as shown in FIG. 8A, an upper barrier film 23 with athickness of about 2 nm having a high relative dielectric constant isformed. That is to say, the upper barrier film 23 is formed of thesilicon-containing HfO₂ film containing nitrogen. The specificcomposition of the upper barrier film 23 is the same as that of theupper barrier film 11 c of the first embodiment.

Next, as shown in FIG. 8B, a polysilicon film 24 serving as a gateelectrode is formed on the upper barrier film 23 by, for example, CVD.Thereafter, the polysilicon film 24, the upper barrier film 23, thesilicon-containing HfO₂ film 22, and the lower barrier film 21 aredry-etched sequentially, using a mask pattern (not shown) covering agate electrode formation region. Thus, as shown in FIG. 8C, a gateelectrode 26 is formed on the silicon substrate 20 via the gateinsulating film 25 having a stacked structure of the lower barrier film21, the silicon-containing HfO₂ film 22, and the upper barrier film 23.Thereafter, ions are implanted into the silicon substrate 20 with thegate electrode 26 as a mask, so that an impurity diffusion layer 27serving as a source region or a drain region is formed. Finally, inorder to activate impurities in the impurity diffusion layers 27, a heattreatment is performed at about 950° C. for about 30 minutes. Theprocesses described above provide a MIS electric field effect transistorhaving the high-k gate insulating film.

As described above, according to the second embodiment, the HfO₂ film22A containing hydrogen is formed on the silicon substrate 20, and thena heat treatment (PDA) is performed with respect to the HfO₂ film 22A todesorb hydrogen, and silicon is diffused in the HfO₂ film 22A throughthe thus formed vacancies so that the silicon-containing HfO₂ film 22 isformed. For this reason, it is possible to allow silicon to be containedefficiently in the HfO₂ film 22A and the vacancies eventually disappearso that the silicon-containing HfO₂ film 22 becomes dense. In this case,as described in the first embodiment, the silicon-containing HfO₂ film22 is hardly crystallized by a high temperature in the productionprocess, so that the silicon-containing HfO₂ film 22 remains mostlyamorphous even after a device is complete. As a result, leak current canbe suppressed from occurring in the gate insulating film 25 having thesilicon-containing HfO₂ film 22, that is, the high-k gate insulatingfilm. Therefore, the thermal stability of the high-k gate insulatingfilm is improved, so that a semiconductor device having excellent heatresistance can be realized and the process margin in the production of asemiconductor device can be increased.

Furthermore, according to the second embodiment, before forming the HfO₂film 22A, the Si₃N₄ film 21A containing hydrogen is formed on thesilicon substrate 20. The Si₃N₄ film 21A is oxidized when forming theHfO₂ film 22A and turns into the SiON film 21B. Thereafter, when theHfO₂ film 22A is subjected to PDA, silicon contained in the SiON film21B is diffused into the HfO₂ film 22A. Moreover, hydrogen is desorbedfrom the SiON film 21B to form vacancies, and Hf contained in the HfO₂film 22A is diffused into the SiON film 21B through the vacancies, sothat the lower barrier film 21 is formed. Therefore, it is ensured thatsilicon can be contained in the HfO₂ film 22A. Furthermore, the HfO₂film 22A or the silicon-containing HfO₂ film 22 can be prevented frombeing reacted with the silicon substrate 20. Furthermore, the lowerbarrier film 21 contains the same metal, Hf as in the silicon-containingHfO₂ film 22, so that the relative dielectric constant of the lowerbarrier film 21 can be high, and thus the relative dielectric constantof the gate insulating film 25 as a whole can be high.

Moreover, according to the second embodiment, the upper barrier film 23is formed by nitriding the surface of the silicon-containing HfO₂ film22 in a process between the process for performing PDA to the HfO₂ film22A and the process for forming the polysilicon film 24 serving as thegate electrode 26. Therefore, the material of the gate electrode 26 andmaterial of the silicon-containing HfO₂ film 22 are prevented fromdiffusing each other. Furthermore, the upper barrier film 23 containsthe same metal, Hf as in the silicon-containing HfO₂ film 22, so thatthe relative dielectric constant of the upper barrier film 23 can behigh, and thus the relative dielectric constant of the gate insulatingfilm 25 as a whole can be high.

Furthermore, according to the second embodiment, the HfO₂ film 22A isformed by CVD that employs a source precursor containing hafnium andhydrogen, so that it is ensured that hydrogen can be contained in theHfO₂ film 22A.

Hereinafter, the features (e.g., mutual diffusion of Hf and Si byhydrogen desorption) and the effect (e.g., improvement of thermalstability) of the process of performing PDA to the HfO₂ film 22A will bedescribed with reference to the drawings showing experiment data or thelike.

FIG. 10 shows the result of measurement by TDS (thermal desorptionspectroscopy) regarding hydrogen that is being desorbed from the HfO₂film by a heat treatment. In FIG. 10, the horizontal axis shows the heattreatment temperature and the vertical axis shows the spectrum intensityof hydrogen gas measured by TDS. As shown in FIG. 10, when the heattreatment temperature reaches about 400° C., first, hydrogen adsorbed onthe surface of the HfO₂ film starts to be desorbed. Thereafter, when theheat treatment temperature reaches about 700° C., hydrogen contained inthe HfO₂ film is desorbed. The density of hydrogen molecules that wascontained in the HfO₂ film just after deposition and eventually desorbedfrom the HfO₂ film by a heat treatment was measured and found to be ashigh as 5.6×10²⁰ molecules/cm². According to the results shown in FIG.10, when the heat treatment temperature is about 700° C., the detectedamount of desorbed hydrogen is largest. Therefore, the optimaltemperature for PDA is about 700° C., and the thus setting allowsexcessive hydrogen contained in the HfO₂ film to be desorbed so that theHfO₂ film can be made dense most effectively.

While performing a heat treatment (temperature increase rate of 10°C./min) in an ultrahigh vacuum with respect to a sample of the HfO₂ filmformed on a Si substrate by CVD with Hf-t-butoxide, which is a liquid Hfsource, the HfO₂ film that was being heated were subjected to in-situobservation to see its changes, using a high resolution cross-sectionalTEM (transmission electron microscope), and the following was confirmed.At room temperature (immediately after the HfO₂ film is formed), aninterface layer (corresponding to the SiON film 21B) that contains alarge number of Si atoms and a small number of Hf atoms is present onthe Si substrate, and the HfO₂ layer that contains a small number of Siatoms and a large number of Hf atoms is present on the interface layer.Thereafter, as the temperature increases, in the temperature range from620° C. to 850° C., a mutual diffusion layer that contains a smallernumber of Si atoms than that of the interface layer and a smaller numberof Hf atoms than that of the HfO₂ layer evidently starts to appearbetween the interface layer and the HfO₂ layer. Finally, when a hightemperature annealing is performed at 860° C., the total physicalthickness of a stacked structure (corresponding to thesilicon-containing HfO₂ film 22) of the HfO₂ layer and the mutualdiffusion layer is larger than that of the HfO₂ layer at the time ofdeposition (room temperature). That is to say, the interface layer iscontracted by expansion of the mutual diffusion layer, and as a result,the relative dielectric constant of the entire Hf silicate stackedstructure including the interface layer becomes high.

In the case of regular PDA, the temperature increase rate is as high as50° C./sec, and the retention period at a heat treatment temperature ofabout 700° C. is as short as 30 seconds, so that the thermal budget(thermal load) is much smaller than that from the in-situ observationduring heating by the high resolution cross-sectional TEM. Therefore,oxidation of the Si substrate caused by PDA occurs only 1 nm or less,and the interface layer becomes very thin because of the mutualdiffusion of Si and Hf so that the final interface layer (correspondingto the lower barrier film 21) is about 0.5 nm. Thus, the relativedielectric constant of the entire Hf silicate stacked structureincluding the interface layer becomes high, and as a result, the EOT ofthe stacked structure as a whole becomes very small. In other words,forming the HfO₂ film by CVD employing a Hf source containing hydrogenis very advantageous as a method for forming a high-k gate insulatingfilm. On the other hand, a HfO₂ film is formed by CVD employing aregular Hf source free from hydrogen, and an in-situ observation duringheating is performed with respect to the HfO₂ film with the highresolution cross-sectional TEM. Then, it was found that mutual diffusionhardly occurred between the interface layer and the HfO₂ layer. As aresult, the thermal stability of the HfO₂ layer was not improved and therelative dielectric constant of the stacked structure of the interfacelayer and the HfO₂ layer was not increased.

FIG. 11 shows the results of C-V measurement after the heat treatmentwith respect to the HfO₂ film containing hydrogen formed by CVDemploying Hf-t-butoxide. More specifically, annealing for activatingimpurities implanted to the gate electrode was performed at 900° C.,950° C. and 1050° C. with respect to samples of a MOS capacitoremploying a HfO₂ film having a physical thickness of 3.0 to 3.3 nm asthe gate insulating film and polysilicon as the gate electrode. Then, agate voltage Vg was applied with a voltage of 0 V set on the substrateside. In FIG. 11, the horizontal axis shows the gate voltage (Vg) andthe vertical axis shows the capacitance. ♦ shows the measured value ofthe capacitance when a heat treatment was performed at 900° C., ▪ showsthe measured value of the capacitance when a heat treatment wasperformed at 950° C., and ▴ shows the measured value of the capacitancewhen a heat treatment was performed at 1050° C.

As shown in FIG. 11, when the HfO₂ film containing hydrogen formed ofHf-t-butoxide is used, stable C-V curve is shown even if the annealingtemperature for activation is increased, and the temperature at whichthe sample can withstand as an ideal MOS capacitor is as high as 1050°C. or more. In other words, in the HfO₂ film containing hydrogen, as aresult of occurrence of significant mutual diffusion of Hf and Siaccompanied by hydrogen desorption caused by PDA, a Si-containing layeris present on the surface side of the HfO₂ film. Therefore, also whenpolysilicon is used as the gate electrode, as shown in FIG. 11, verystable heat resistance is exhibited at about 1050° C.

FIG. 12 shows the result of C-V measurement after a heat treatment withrespect to a HfO₂ film free from hydrogen formed by CVD employing asource free from hydrogen, specifically, Hf-nitrato (Hf(NO₃)₄) as acomparative example. More specifically, annealing for activatingimpurities implanted to the gate electrode was performed at 900° C.,950° C. and 1150° C. with respect to samples of a MOS capacitoremploying a HfO₂ film having a physical thickness of 3.0 to 3.3 nm asthe gate insulating film and polysilicon as the gate electrode. Then, agate voltage Vg was applied with a voltage of 0 V set on the substrateside. In FIG. 12, the horizontal axis shows the gate voltage (Vg) andthe vertical axis shows the capacitance. ▪ shows the measured value ofthe capacitance when a heat treatment was performed at 900° C., ♦ showsthe measured value of the capacitance when a heat treatment wasperformed at 950° C., and ▴ shows the measured value of the capacitancewhen a heat treatment was performed at 1150° C.

As shown in FIG. 12, when the HfO₂ film free from hydrogen formed ofHf-nitrato is used, the temperature at which the sample can withstand asan ideal MOS capacitor is at most 900° C. Taking the results shown inboth FIGS. 11 and 12 into consideration, the thermal stability guaranteetemperature when the HfO₂ film containing hydrogen is used is 1050° C.or more, whereas the thermal stability guarantee temperature when theHfO₂ film free from hydrogen is used is about 900° C. In other words,using the HfO₂ film containing hydrogen improves the thermal stabilityguarantee temperature by 150° C. or more.

FIG. 13 shows the results of comparison in the thermal stability betweenthe case where a HfO₂ film containing hydrogen was used and the casewhere a HfO₂ film free from hydrogen was used in a MOS capacitor havinga stacked structure of Si substrate/SiN film/HfO₂ film/polysilicon film.More specifically, annealing for activation was performed attemperatures in the range from 900° C. to 1150° C. for 30 seconds in anitrogen atmosphere with respect to each MOS capacitor sample. Then, agate voltage (V_(G)) of −1.0 V was applied with a voltage of 0 V set onthe substrate side, and leak current J_(G) was measured. The HfO₂ filmcontaining hydrogen was formed of Hf-t-butoxide, and the HfO₂ film freefrom hydrogen was formed of a source free from hydrogen. In FIG. 13, thehorizontal axis shows the activation annealing temperature, and thevertical axis shows the leak current J_(G). ♦ shows the measured valueof the leak current J_(G) when a source free from hydrogen is used, and□ shows the measured value of the leak current J_(G) when Hf-t-butoxidewas used.

As shown in FIG. 13, when the HfO₂ film containing hydrogen formed ofHf-t-butoxide was used and the annealing temperature for activation wasincreased, an increase of the leak current J_(G) could be restricted toonly one order. On the other hand, in the case where the HfO₂ film freefrom hydrogen was used and the annealing temperature for activation wasincreased, the leak current J_(G) was increased by about three orders,that is, about 1000 times larger than in the case of the HfO₂ filmcontaining hydrogen. In other words, using the HfO₂ film containinghydrogen can reduce the defect production probability to about 1/1000 ofthat in the case where the HfO₂ film free from hydrogen.

Each of the HfO₂ film containing hydrogen and the HfO₂ film free fromhydrogen was deposited on a silicon substrate to the same physicalthickness (3 nm), and the EOT of the HfO₂ film including the interfacelayer was measured. The results were as follows. The EOT was 1.1 nm whenthe HfO₂ film containing hydrogen was deposited, and the EOT was 1.6 nmwhen the HfO₂ film free from hydrogen was deposited. That is to say, therelative dielectric constant when the HfO₂ film containing hydrogen wasdeposited was about 1.46 times higher than that when the HfO₂ film freefrom hydrogen was deposited. This is caused by the fact that when theHfO₂ film containing hydrogen was deposited, Si and Hf are diffusedmutually between the interface layer and HfO₂ layer so that Hf iscontained in the interface layer, and consequently the relativedielectric constant in the interface layer portion is reducedsignificantly.

A HfO₂ film containing hydrogen having a thickness of 3.5 nm was formedon a silicon substrate, and then a PDA treatment (800° C., 30 seconds)was performed with respect to the HfO₂ film. Thereafter, Si, 0 and Hfwere measured from the surface side of the HfO₂ film by XPS (X-rayphotoelectron spectroscopy) using MgKa radiation and the composition ofthe HfO₂ film after the PDA treatment was found to be 0.6 for Hf, 0.49for Si and 2.0 for O. It should be noted that since primarily thesurface of the HfO₂ film was observed for measurement by the XPStechnique, the detection depth was set to about 2 to 3 nm by detectingphotoelectrons having an escape angle of 57 degrees with respect to thesurface of the substrate. The results as described above indicate thatin the HfO₂ film after the PDA treatment, Si has been diffused up to thevicinity of the surface.

FIG. 14 shows the relationship between the physical thickness of theHfO₂ film immediately after being formed and the leak current after aMOS capacitor was complete in the case where PDA was performed withrespect to the HfO₂ film (containing hydrogen), which is the insulatingfilm of the MOS capacitor. More specifically, after a HfO₂ filmcontaining hydrogen was formed by CVD, PDA was performed to the HfO₂film in a nitrogen atmosphere at pressure of about 60000 Pa (450 torr)at 800° C. for 30 seconds. Thereafter, a polysilicon film that was toserve as a gate electrode was deposited. Then, after ions were implantedinto the polysilicon film, annealing for activation is performed in anitrogen atmosphere at a pressure of about 110000 Pa (760 torr) at 900°C. for 30 seconds. Thereafter, a gate voltage (V_(G)) of −1.0 V wasapplied with 0 V on the substrate side, and the leak current J_(G) wasmeasured. The physical thickness of the HfO₂ film immediately afterbeing formed is measured by an ellipsometry method (polarizationmethod). For comparison, with respect to samples of MOS capacitorsobtained by omitting the process of performing PDA with respect to theHfO₂ film, the relationship between the physical thickness of the HfO₂film immediately after being formed and the leak current after the MOScapacitor was produced was investigated.

As shown in FIG. 14, when PDA is performed, a smaller leak current J_(G)is achieved than when PDA is not performed. This seems to be caused forthe reason as follows: Si is diffused to the HfO₂ film by the PDA, whichprevents the HfO₂ film from being crystallized by annealing foractivation, therefore the HfO₂ film in the finished MOS capacitorremains mostly amorphous, so that the gate leak current can besuppressed from increasing. Furthermore, it seems that the gate leakcurrent has been reduced also by the fact that a reaction between theelectrode material and the material of the high dielectric constant filmhas been suppressed by achieving a dense silicon-containing HfO₂ film.As shown in FIG. 14, the effect of suppressing the gate leak current inthe case where PDA is performed is exhibited more significantly as thephysical thickness of the HfO₂ film is smaller. The above results haveconfirmed that it is very important to provide a process of performingPDA (post deposition anneal) with respect to the high dielectricconstant film after the high dielectric constant film that will serve asa gate insulating film is deposited and before a gate electrode isformed in order to reduce the leak current effectively.

In the second embodiment, a polysilicon film 24 is used as the gateelectrode 26, but a metal film can be used instead. For example, thesurface of the silicon-containing HfO₂ film 22 is nitrided, and then aTiN film and an Al film that will serve as the gate electrode 26 may bedeposited sequentially by sputtering. Alternatively, after the surfaceof the silicon-containing HfO₂ film 22 is nitrided, a Ta film that willserve as the gate electrode 26 may be deposited. Alternatively, a TiNfilm, a TaN film or the like may be deposited without nitriding thesurface of the silicon-containing HfO₂ film 22. In this case, Si or Gecan be mixed with the Ti film, the TaN film or the like. When a metalfilm is used as the gate electrode 26 as described above, after themetal film is formed, defects in the gate insulating film 25 can bereduced further by further applying a heat treatment (PMA: postmetalization anneal). When a C-V measurement is performed with respectto the thus formed MOS structure, it is confirmed that the amount of thedefects in the insulating film and the corresponding hysteresis arereduced. A temperature of 700° C. or more is effective as thetemperature of PMA. When annealing is performed in a gas containinghydrogen at 450° C. for about 30 minutes, the interface state in thegate insulating film 25 can be reduced.

In the second embodiment, a HfO₂ film is used as the high dielectricconstant material constituting the gate insulating film 25, ZrO₂, TiO₂,Ta₂O₅, La₂O₃, CeO₂, Al₂O₃, or BST (barium strontium titanium oxide) canbe used instead. Alternatively, ternary oxide such as Hf_(x)Al_(y)O₂,where x>0 and y>0) can be used. Alternatively, metal silicate in whichSi atoms are contained in metal oxide as described above can be used. Inany case, the effect of mutual diffusion in the high dielectric constantfilm containing hydrogen can be realized regardless of the compositionor the constituent materials at the time of the deposition of the highdielectric constant film.

In the second embodiment, the HfO₂ film 22A is deposited by CVDemploying Hf-t-butoxide, which is a liquid Hf source precursor. However,instead of this, when CVD is used, other Hf source precursors containinghydrogen and hafnium such as tetrakis diethylamido hafnium, (TDEAH:C₁₆H₄₀N₄Hf), tetrakis dimethylamino hafnium (TDMAH: C₁₆H₃₆HfO₄), ortetrakis 1-methoxy-2-methyl-2-propoxy hafnium (Hf(MMP)₄:Hf[OC(CH₃)₂CH₂OCH₃]₄) can be used. Alternatively, a HfO₂ film can beformed by CVD employing a solid Hf source precursor such as Hf-nitrato(Hf(NO₃)₄) and a source gas containing hydrogen such as hydrogen gas.Alternatively, when PVD (physical vapor deposition) such as sputteringis used, a target containing hafnium can be used in an atmospherecontaining hydrogen. More specifically, a hafnium target can be used inan atmosphere containing oxygen gas and argon gas to which hydrogen gasis added, or a hafnium oxide target can be used in an atmospherecontaining argon gas to which hydrogen gas is added. Hydrogen gas isadded for hydrogen to be captured in the high dielectric constant film(HfO₂ film).

In the second embodiment, hydrogen is captured in the HfO₂ film 22A orthe Si₃N₄ film 21A as a predetermined substance (substance for vacancyformation), but instead of this, for example, chlorine, fluorine, oriodine can be captured using a halogen-based gas. Any substances can beused as the substance for vacancy formation, as long as it can bedesorbed from the HfO₂ film 22A or the Si₃N₄ film 21A in the form of gasat a temperature of about 600 to 850° C. and can promote the diffusionof Hf or Si through the thus formed vacancies. Furthermore, thesubstance for vacancy formation for the HfO₂ film 22A may be differentfrom that for the Si₃N₄ film 21A.

In the second embodiment, the Si₃N₄ film 21A, that is, the lower barrierfilm 21 can be formed by performing, for example, thermal nitridation orplasma nitridation in a gas containing nitrogen with respect to thesilicon substrate 20. Alternatively, the SiON film 21B can be directlyformed by nitriding the surface of the silicon substrate 20 with N₂O gasbefore forming the HfO₂ film 22A without forming the Si₃N₄ film 21A.Alternatively, the high dielectric insulating film containing nitrogenthat will become the lower barrier film 21 can be directly formed on thesilicon substrate 20 by introducing a gas containing nitrogen in theearly stage of the formation of the HfO₂ film 22A by evaporation.

In the second embodiment, the upper barrier film 23 can be formed byperforming, for example, thermal nitridation or plasma nitridation in agas containing nitrogen with respect to the silicon-containing HfO₂ film22. Alternatively, the upper barrier film 23 can be formed by nitridingthe surface of the silicon-containing HfO₂ film 22 by introducingnitrogen gas in the early stage of the formation of the polysilicon film24 that will serve as the gate electrode 26. Alternatively, the highdielectric insulating film containing nitrogen that will become theupper barrier film 23 can be formed on the side of the surface of theHfO₂ film 22A by introducing a gas containing nitrogen in the finalstage of the formation of the HfO₂ film 22A by evaporation.

In the second embodiment, PDA is performed with respect to the HfO₂ film22A to form the silicon-containing HfO₂ film 22, and then the upperbarrier film 23 is formed by nitriding the surface of thesilicon-containing HfO₂ film 22. However, instead of this, after theupper barrier film 23 is formed by nitriding the surface of the HfO₂film 22A, PDA is performed with respect to the HfO₂ film 22A to form thesilicon-containing HfO₂ film 22.

In the second embodiment, the entire stacked structure of the lowerbarrier film 21, the silicon-containing HfO₂ film 22 and the upperbarrier film 23 may contain nitrogen.

In the second embodiment, it is preferable that in the process shown inFIG. 7B, first, a source such as evaporated Hf-t-butoxide is suppliedinto a chamber, and then oxygen gas is supplied to the chamber, andthereafter the temperature in the chamber is increased from roomtemperature and kept in a predetermined temperature range of about 300to 500° C. This makes it possible that Hf molecules are adsorbed rapidlyon the silicon substrate 20 at a low temperature, so that the HfO₂ film22A can be formed uniformly. Furthermore, the incubation time from thestart of the supply of the source gas to the start of crystal growth ofthe HfO₂ film can be shortened. Furthermore, the interface layer (SiONfilm 21B) formed between the HfO₂ film 22A and the silicon substrate 20can be thin.

In the second embodiment, it is preferable that the temperature for theheat treatment in PDA in the process shown in FIG. 7C is 600° C. or moreand 850° C. or less. This ensures that hydrogen can be desorbed from theHfO₂ film 22A and thus silicon can be diffused in the HfO₂ film 22A.

In the second embodiment, it is preferable to satisfyT≦6.69·y/(x+y)+749.4, where the composition of the silicon-containingHfO₂ film 22 is expressed as Hf_(x)Si_(y)O, where x>0, and y>0, and themaximum temperature in the production process is expressed as T [° C.].This ensures the thermal stability of the gate insulating film 25 havingthe silicon-containing HfO₂ film 22. When the gate electrode 26 is madeof a material containing silicon, it is preferable to satisfyT≦6.69·y/(x+y)+749.4, and y/(x+y)≦0.30. This ensures the thermalstability and the reliability of the gate insulating film 25 having thesilicon-containing HfO₂ film 22.

The invention may be embodied in other forms without departing from thespirit or essential characteristics thereof. The embodiments disclosedin this application are to be considered in all respects as illustrativeand not limiting. The scope of the invention is indicated by theappended claims rather than by the foregoing description, and allchanges which come within the meaning and range of equivalency of theclaims are intended to be embraced therein.

1. A semiconductor device, comprising: a gate insulating film formed ona substrate; and a gate electrode formed on the gate insulating film;the gate insulating film comprising: a high dielectric constant filmcontaining a metal, oxygen and silicon; and a lower barrier film formedbelow the high dielectric constant film and containing the metal,oxygen, silicon and nitrogen, wherein023≦y/(x+y)≦0.90 when a composition of the high dielectric constant filmis expressed as M_(x)Si_(y)O, where M, O and Si represent the metal,oxygen and silicon, respectively, and x>0 and y>0.
 2. The semiconductordevice according to claim 1, wherein the gate insulating film comprisesan upper barrier film formed above the high dielectric constant film,and the upper barrier film contains the metal, oxygen and nitrogen. 3.The semiconductor device according to claim 1, wherein the gateinsulating film comprises an upper barrier film formed above the highdielectric constant film, and the upper barrier film contains the metal,oxygen, silicon and nitrogen.
 4. The semiconductor device according toclaim 1, wherein the gate electrode is a metal gate electrode.
 5. Thesemiconductor device according to claim 1, wherein the lower barrierfilm is a silicon oxynitride film including the metal.
 6. Thesemiconductor device according to claim 1, wherein the high dielectricconstant film contains nitrogen.
 7. A semiconductor device, comprising:a gate insulating film formed on a substrate; and a gate electrodeformed on the gate insulating film; the gate insulating film comprising:a high dielectric constant film containing a metal, oxygen and silicon;and a lower barrier film formed below the high dielectric constant filmand containing the metal, oxygen, silicon and nitrogen, wherein0.23≦y/(x+y)≦0.30 when a composition of the high dielectric constantfilm is expressed as M_(x)Si_(y)O, where M, O and Si represent themetal, oxygen and silicon, respectively, and x>0 and y>0.
 8. Asemiconductor device, comprising: a gate insulating film formed on asubstrate; and a gate electrode formed on the gate insulating film; thegate insulating film comprising: a high dielectric constant filmcontaining a metal, oxygen and silicon; and a lower barrier film formedbelow the high dielectric constant film and containing the metal,oxygen, silicon and nitrogen, whereinx/(x+y)≦0.10 when the metal is hafnium or zirconium, and a compositionof the lower barrier film is expressed as M_(x)Si_(y)O_(z)N_(w), whereM, O, Si and N represent the metal, oxygen, silicon and nitrogen,respectively, and x>0, y>0, z>0 and w>0.
 9. The semiconductor deviceaccording to claim 1, wherein the lower barrier film is amorphous. 10.The semiconductor device according to claim 1, wherein the gateelectrode is a polysilicon electrode.
 11. The semiconductor deviceaccording to claim 1, wherein the gate electrode is made of a materialcontaining silicon.
 12. The semiconductor device according to claim 1,wherein the high dielectric constant film contains chlorine.
 13. Thesemiconductor device according to claim 1, wherein the high dielectricconstant film contains fluorine.
 14. The semiconductor device accordingto claim 1, wherein the high dielectric constant film contains hydrogen.15. The semiconductor device according to claim 1, wherein the highdielectric constant film contains iodine.
 16. The semiconductor deviceaccording to claim 1, wherein the high dielectric constant film containscarbon.
 17. The semiconductor device according to claim 1, wherein thehigh dielectric constant film is amorphous.
 18. The semiconductor deviceaccording to claim 17, wherein the high dielectric constant filmcontains nitrogen.
 19. The semiconductor device according to claim 18,wherein the high dielectric constant film contains crystallites.
 20. Thesemiconductor device according to claim 2, wherein the upper barrierfilm is amorphous.
 21. The semiconductor device according to claim 1,wherein the high dielectric constant film includes a part which islocated 1 through 2 nm apart from the gate electrode and which is Hfsilicate containing nitrogen.
 22. A semiconductor device, comprising: agate insulating film formed on a substrate; and a gate electrode formedon the gate insulating film; the gate insulating film comprising: a highdielectric constant film containing a metal, oxygen and silicon, wherein0.23≦y/(x+y)≦0.90 when a composition of the high dielectric constantfilm is expressed as M_(x)Si_(y)O, where M, O and Si represent themetal, oxygen and silicon, respectively, and x>0 and y>0.
 23. Thesemiconductor device according to claim 22, wherein the high dielectricconstant film contains nitrogen.
 24. The semiconductor device accordingto claim 22, wherein the gate insulating film comprises a lower barrierfilm formed below the high dielectric constant film, and the lowerbarrier film contains the oxygen, silicon and nitrogen.
 25. Asemiconductor device according to claim 22, wherein the gate insulatingfilm comprises an upper barrier film formed above the high dielectricconstant film, and the upper barrier film contains the metal, oxygen andnitrogen.
 26. A semiconductor device according to claim 22, wherein thegate insulating film comprises an upper barrier film formed above thehigh dielectric constant film, and the upper barrier film contains themetal, oxygen, silicon and nitrogen.
 27. The semiconductor deviceaccording to claim 7, wherein the high dielectric constant film containsnitrogen.
 28. The semiconductor device according to claim 8, wherein thehigh dielectric constant film contains nitrogen.
 29. The semiconductordevice according to claim 1, wherein the metal in the high dielectricconstant film is at least one of hafnium or zirconium.
 30. Thesemiconductor device according to claim 1, wherein the metal in the highdielectric constant film is at least one of hafnium, zirconium,titanium, tantalum, lanthanum, cerium, or aluminum.
 31. Thesemiconductor device according to claim 14, wherein 5×10²⁰ to 4×10²¹hydrogen atoms/cm³ were contained in the high dielectric constant film.32. The semiconductor device according to claim 17, wherein 3×10¹⁹ to4×10²⁰ carbon atoms/cm³ were contained in the high dielectric constantfilm.